In a nuclear reactor power plant, a nuclear reactor vessel is used to generate heat for the production of steam and electricity. The reactor vessel is typically a pressure vessel which encloses a core of nuclear fuel and cooling water which is often borated water.
In order to monitor the operating conditions within the pressure vessel, instrumentation devices are often introduced into the nuclear core through ports or penetrations in the vessel. Some of these penetrations are provided through the reactor vessel closure head.
The closure head may also provide for the penetration of drive mechanisms of control rods, which are used to regulate the rate of nuclear reactions which take place within the core, and which control the power output of the plant.
Although these ports are mechanically sealed to prevent the inadvertent leakage of coolant from the reactor vessel, the operating conditions of a nuclear reactor pressure vessel require additional safeguards. Typically, the pressure vessel maintains the coolant therein at an internal pressure of about 15 MPa (2250 psi) and at a temperature of about 315.degree. C. (600.degree. F.). Because of such an enlarged internal pressure, reactor coolant may leak from the mechanical joint of these penetrations, or when the control rods are withdrawn.
The coolant within a reactor vessel is typically acidic and highly corrosive due to the presence of boric acid which is dissolved within the coolant. Boric acid is a neutron absorber which is used as a variable reactivity control over the long-term operation of the plant. Even though there are regulatory limits on the allowable amounts of coolant which may be emitted from the reactor vessel, components on the exterior of and in close proximity to, the reactor vessel head need to be periodically inspected to determine if coolant is being emitted.
Because an operating nuclear reactor generates an irradiated environment, the inspection and/or maintenance of the reactor vessel is typically conducted at times when the reactor is shut down for normal inspection or maintenance procedures, such as, the refueling of the core. A usual tell-tale sign of the presence of a leak in this area is white boric acid crystal deposits on the reactor vessel head. Any of several methods for determining the presence of a possible leak source may be used, but verification of the existence of a leak, estimation of its size, and the identification of its location is best done visually.
Generally, control rod drive mechanisms and instrumentation ports are enclosed by a cooling shroud. The shroud provides protection for the drive mechanisms, as well as a means for directing the flow of air around the ports for natural circulation, thereby cooling of the ports and drive mechanisms. This can make it even more difficult to visually detect the presence of borated coolant in this area as well as perforations in the shroud of the reactor.
A number of patents are directed to nuclear power plant inspection and inspection devices and in particular, devices for inspecting nuclear reactors. U.S. Pat. No. 4,857,261 to Marshall discloses a monitoring system for use in a nuclear reactor head area. The monitoring system disclosed in the Marshall patent comprises a plurality of video cameras attached to a cooling shroud on the vessel head. A right-angle lens is attached to each video camera and a halogen light source is attached to the shroud adjacent to each video camera to provide adequate lighting.
U.S. Pat. No. 3,780,571 to Wiesener discloses a device for inspecting nuclear reactor pressure vessels, which can be removed from the vessel when the vessel is in service and later replaced in the same position to make inspections. The device includes means for handling inspection of equipment, such as cameras, ultrasonic detectors or the like, and is moveable in several motions to permit it to operate in all areas of the vessel.
U.S. Pat. No. 4,311,556 to Iwamoto discloses a system for the inspection of the inside of a nuclear reactor vessel which utilizes a working unit and monitor for monitoring the movement of the working unit by a manipulator. The manipulator is a 2-arm structure, one of which is equipped with a working unit and the other of which is equipped with a television camera to continuously image the condition of the working unit.
U.S. Pat. No. 4,460,920 discloses an automatic traveling tube-interior manipulator for the remotely controlled transportation of testing devices and tools along given feed paths. The manipulator has a stepping mechanism that enables it to traverse narrow tube elbows or even vertical tube sections so that the test device tools attached to the manipulator head can be positioned and moved along their feed paths.
U.S. Pat. No. 4,643,867 to Hornak, et al. discloses a mounting system for a set of four television cameras upon a nuclear reactor refueling machine outer or stationery mast. The television cameras scan the reactor core fuel assemblies as they are being vertically removed from the core by the refueling machine during the performance of the refueling operation. In the alternative, the television cameras provide remote viewing of the reactor core in order to facilitate insertion of the fuel assemblies into the core during a refueling operation.
U.S. Pat. No. 4,656,509 to Matsuyama discloses a water leakage monitoring system for remotely monitoring leakages of water from monitored members and equipment disposed in a plant. The drive of the Matsuyama patent comprises a remotely controlled carriage which intermittently travels along an inspection route, a television camera hung from the carriage so as to monitor water leakage through each of the monitored members along the inspection path through the operation of an attitude adjusting mechanism in response to an attitude control signal. A coating composition applied to the surface of each of the monitored members changes in color when it is wet with water leaked through the associated member.
U.S. Pat. No. 4,661,308 to Tokinaka discloses a remote-controlled mobile inspecting and monitoring system which comprises a rail laid along an inspection route, power lines provided along the rail, and an inspection vehicle carrying inspecting and monitoring equipment to move along the rail. A power receiving unit mounted on the inspection vehicle is connected to the power lines such that the inspection vehicle carries a battery unit for supplying power to on board equipment and a change over unit for controlling the power receiving unit so as to be connected to or disconnected from the power lines. The system is capable of reducing the load on the battery unit by receiving power through the power receiving unit from the power lines so that a battery unit of reduced capacity is needed, thereby making it possible to reduce the size of the inspection vehicle.
U.S. Pat. No. 4,668,981 to Egger discloses a system for performing visual inspection of water-immersed portions of a nuclear reactor vessel. The system utilizes the manual manipulation of a television camera through which the reactor components are viewed. A television camera is suspended within the reactor vessel from a first hand held line by an individual positioned on a platform above the open top of the vessel. The camera is carried on a positioning device which includes a pair of arms extending outwardly to terminal ends on opposite sides of the camera axis. Lines attached to each of these arms are held by a second individual, also positioned on the platform, at a distance from the first individual. A third individual is positioned at a television monitor to view the image relayed by the camera, and to direct the other two individuals in its deployment.
U.S. Pat. No. 4,702,878 to Klug, et al, discloses an apparatus for remotely inspecting and cleaning areas between the tubes on a tube sheet in a nuclear steam generator. A flexible tube is connected to one end of the sled and has at its other end extending out through an opening. The tube is of sufficient length to be freely movable into and out of the shell opening to move the sled along the periphery of the tube sheet. A probe such as a television camera or a fiberscope and a gripper are mounted on the sled for searching and retrieving objects.
Finally, U.S. Pat. No. 4,729,423 to Martin discloses a process and apparatus for optically checking the shape and dimensions of the ends of the tubes of a steam generator. A photographic camera is placed parallel to the tubular plate inside the water tank and exposures are made with the camera in different positions so as to obtain at least two views at different angles of the tubes which have to be checked.
None of the prior art discussed above discloses a nuclear reactor inspection device which can fully inspect a reactor head and which can be used in association with a plurality of movable members which permit the complete visual inspection of the reactor and reactor head. It would be desirable to provide a nuclear reactor inspection device which can easily inspect the reactor head of a nuclear reactor and which can be utilized to inspect selected portions of a reactor head including the control rod drive mechanism penetrations, the thermal sleeves, the funnels, and the annulus between the control rod drive mechanism and the thermal sleeves.
It would be particularly desirable to provide a nuclear reactor head inspection system which can rotate a full 360.degree. and which can provide for full vertical and horizontal visibility and movement of a camera and light assembly. The present invention is directed to overcome the problems associated with prior art devices for inspecting the reactor head of a nuclear power plant. The objects and benefits of the present invention will become apparent from the detailed description and summary which follow.